Fluid pressure transmission pill

ABSTRACT

A pill for wellbore operations, that includes a base fluid; and at least two polymers that interact to form a gelatinous structure characterized as isolating and controllably transmitting hydrostatic pressure between a first wellbore fluid above the pill in a wellbore and a second wellbore fluid below the pill in the wellbore is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Patent Application No.60/909,895, filed on Apr. 3, 2007, which is herein incorporated byreference in its entirety.

BACKGROUND OF INVENTION

1. Field of the Invention

Embodiments disclosed herein relate generally to pills for wellboreoperations. In particular, embodiments disclosed herein related to pillshaving a gelatinous structure.

2. Background Art

When drilling or completing wells in earth formations, various fluidstypically are used in the well for a variety of reasons. Common uses forwell fluids include: lubrication and cooling of drill bit cuttingsurfaces while drilling generally or drilling-in (i.e., drilling in atargeted petroliferous formation), transportation of “cuttings” (piecesof formation dislodged by the cutting action of the teeth on a drillbit) to the surface, maintaining well stability, suspending solids inthe well, fracturing the formation in the vicinity of the well,displacing the fluid within the well with another fluid, cleaning thewell, testing the well, transmitting hydraulic horsepower to the drillbit, fluid used for emplacing a packer, abandoning the well or preparingthe well for abandonment, and otherwise treating the well or theformation. Further, fluid in the annulus provides a static head whichassists in maintaining the hydrostatic equilibrium in the wellbore,thereby controlling formation fluid pressure to prevent blowouts andminimizing fluid loss into and stabilizing the formation through whichthe well is being drilled

Many difficulties in drilling are due to the wellbore pressure deviatingoutside of the pressure gradient window during a particular drillingoperation. As a result, the use managed pressure drilling (MPD)techniques has increased as a way to reduce or prevent rig down time. InMPD, the annular pressures in drilling and completing a well areaccurately controlled. As a well is drilled, the circulation of thewellbore fluid may be used to achieve the desired bottom hole pressure.However, in a static well, the pressure is solely determined by thehydrostatic pressure of the wellbore fluid.

Further, in MPD, a closed loop circulation system is generally used,combing hydrostatic pressure control with frictional pressure control. Alower mud weight is typically used, and a secondary choke is applied tocreate a combined annular pressure profile within the well.

Accordingly, there exists a continuing need to developments in accuratecontrol of pressures in a wellbore.

SUMMARY OF INVENTION

In one aspect, embodiments disclosed herein relate to a pill forwellbore operations, that includes a base fluid; and at least twopolymers that interact to form a gelatinous structure characterized asisolating and controllably transmitting hydrostatic pressure between afirst wellbore fluid above the pill in a wellbore and a second wellborefluid below the pill in the wellbore.

In another aspect, embodiments disclosed herein relate to method of awellbore operation that includes emplacing a first wellbore fluid in awellbore; spotting a pill to a region within the emplaced first wellborefluid; and allowing the spotted pill to viscosify and separate the firstwellbore fluid into an upper section and a lower section, wherein theviscosified pill is a gelatinous structure characterized as isolatingand controllably transmitting hydrostatic pressure between the two fluidsections.

In yet another aspect, embodiments disclosed herein relate to a processfor completing a well that includes emplacing a first wellbore fluidhaving a first density in a wellbore; spotting a pill to a region withinthe emplaced first wellbore fluid; allowing the spotted pill toviscosify and separate the first wellbore fluid into an upper sectionand a lower section, wherein the viscosified pill is a gelatinousstructure characterized as isolating and controllably transmittinghydrostatic pressure between two fluid sections; and emplacing a secondwellbore fluid having a second density greater than the first density inthe wellbore, wherein the emplacement of the second wellbore fluiddisplaces at least a portion of the upper section of first wellborefluid.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is graph of the wire line logs of an exemplary well in accordancewith an embodiment of the present disclosure.

DETAILED DESCRIPTION

In one aspect, embodiments disclosed herein relate to a pill forwellbore operations. In particular, embodiments disclosed herein relatedto a pill having a gelatinous structure, whereby the pill may isolateand controllably transmit hydrostatic pressure between two fluids oneither side of the pill.

In one embodiment, a pill of the present disclosure may be formed from abase fluid and at least two polymers that interact to form a gelatinousstructure that may isolate and controllably transmit hydrostaticpressure between two fluids on either side of the pill. As used herein,isolation of two fluids refers to the avoidance of channeling betweenthe two fluids separated by the pill, for example, channeling of alighter fluid into a denser fluid. Further, as also used herein, theterm controllably implies that the pill allows for a user to assist inpressure management of a well, not that absolute control is necessarilypresent.

In a particular embodiment, a pill of the present disclosure haselastomeric properties. In another embodiment, the pill of the presentdisclosure is substantially solids-free.

Base Fluid

In various embodiments of the present disclosure, the pill may be awater-based fluid, an invert emulsion, or an oil-based pill.

Water-based pills may have an aqueous fluid as the base fluid. Theaqueous fluid may include at least one of fresh water, sea water, brine,mixtures of water and water-soluble organic compounds and mixturesthereof. For example, the aqueous fluid may be formulated with mixturesof desired salts in fresh water. Such salts may include, but are notlimited to alkali metal chlorides, hydroxides, or carboxylates, forexample. In various embodiments of the drilling fluid disclosed herein,the brine may include seawater, aqueous solutions wherein the saltconcentration is less than that of sea water, or aqueous solutionswherein the salt concentration is greater than that of sea water. Saltsthat may be found in seawater include, but are not limited to, sodium,calcium, sulfur, aluminum, magnesium, potassium, strontium, silicon,lithium, and phosphorus salts of chlorides, bromides, carbonates,iodides, chlorates, bromates, formates, nitrates, oxides, and fluorides.Salts that may be incorporated in a brine include any one or more ofthose present in natural seawater or any other organic or inorganicdissolved salts. Additionally, brines that may be used in the drillingfluids disclosed herein may be natural or synthetic, with syntheticbrines tending to be much simpler in constitution. In one embodiment,the density of the drilling fluid may be controlled by increasing thesalt concentration in the brine (up to saturation). In a particularembodiment, a brine may include halide or carboxylate salts of mono- ordivalent cations of metals, such as cesium, potassium, calcium, zinc,and/or sodium.

The oil-based/invert emulsion pills may include an oleaginous continuousphase and a non-oleaginous discontinuous phase for the base fluid. Theoleaginous fluid may be a liquid, more preferably a natural or syntheticoil, and more preferably the oleaginous fluid is selected from the groupincluding diesel oil; mineral oil; a synthetic oil, such as hydrogenatedand unhydrogenated olefins including polyalpha olefins, linear andbranch olefins and the like, polydiorganosiloxanes, siloxanes, ororganosiloxanes, esters of fatty acids, specifically straight chain,branched and cyclical alkyl ethers of fatty acids; similar compoundsknown to one of skill in the art; and mixtures thereof. Theconcentration of the oleaginous fluid should be sufficient so that aninvert emulsion forms and may be less than about 99% by volume of theinvert emulsion. In one embodiment, the amount of oleaginous fluid isfrom about 30% to about 95% by volume and more preferably about 40% toabout 90% by volume of the invert emulsion fluid. The oleaginous fluid,in one embodiment, may include at least 5% by volume of a materialselected from the group including esters, ethers, acetals,dialkylcarbonates, hydrocarbons, and combinations thereof.

The non-oleaginous fluid used in the formulation of the invert emulsionbase fluid disclosed herein is a liquid and may be an aqueous liquid. Inone embodiment, the non-oleaginous liquid may be selected from the groupincluding sea water, a brine containing organic and/or inorganicdissolved salts, liquids containing water-miscible organic compounds,and combinations thereof. The amount of the non-oleaginous fluid istypically less than the theoretical limit needed for forming an invertemulsion. Thus, in one embodiment, the amount of non-oleaginous fluid isless that about 70% by volume, and preferably from about 1% to about 70%by volume. In another embodiment, the non-oleaginous fluid is preferablyfrom about 5% to about 60% by volume of the invert emulsion fluid. Thus,in various embodiments, the base fluid phase may include either anaqueous fluid or an oleaginous fluid, or mixtures thereof.

Gelatinous Structure

The gelatinous structure of the pill of the present disclosure may beformed as a result of polymer interactions, such as ionic interactionsand/or crosslinking, between two polymers. The resulting gelatinousstructure may be characterized as having the ability to isolate andcontrollably transmit hydrostatic pressure between two fluids. Invarious embodiments, the two polymers used to form the gelatinousstructure may be identical or similar in structure or may have distinctchemical structures.

Various types of polymers that may be used to form the gelatinousstructure of the present disclosure include various natural or syntheticpolymers. Examples of polymers that may be used in the pill of thepresent disclosure include typical natural polymers and derivatives suchas xantham gum, diutan, hydroxyethyl cellulose (HEC), or otherpolysaccharide or polysaccharide derivatives or synthetic polymers andoligomers such as poly(ethylene glycol) [PEG], poly(diallyl amine),poly(acrylamide), poly(aminomethylpropylsulfonate) [AMPS polymer],poly(acrylonitrile), poly(vinyl acetate), poly(vinyl alcohol),poly(vinyl amine), poly(vinyl sulfonate), poly(styryl sulfonate),poly(acrylate), poly(methyl acrylate), poly(methacrylate), poly(methylmethacrylate), poly(vinylpyrrolidone), poly(vinyl lactam) and co-, ter-,and quater-polymers of the following co-monomers: ethylene, butadiene,isoprene, styrene, divinylbenzene, divinyl amine, 1,4-pentadiene-3-one(divinyl ketone), 1,6-heptadiene-4-one (diallyl ketone), diallyl amine,ethylene glycol, acrylamide, AMPS, acrylonitrile, vinyl acetate, vinylalcohol, vinyl amine, vinyl sulfonate, styryl sulfonate, acrylate,methyl acrylate, methacrylate, methyl methacrylate, vinylpyrrolidone,vinyl lactam, and aliphatic amine polymers including polyetheramines andpolyethylenimines.

In another embodiment, at least one of the polymers may be an aliphaticamine such as polyetheramine. Example of polyetheramine include thosecommercially available under the trade name Jeffamine® HuntsmanPerformance Products (Woodlands, Tex.). For example, useful Jeffamine®products may include triamines Jeffamine® T-5000 and Jeffamine® T-3000or diamines such as Jeffamine® D-400 and Jeffamine® D-2000. Usefulpolyetheramines may possess a repeating polyether backbone and may varyin molecular weight from about 200 to about 5000 g/mol. In variousembodiments, a polyetheramine may be used as a crosslinking agent tocrosslink a natural or synthetic polymer. While reference to onlypolyetheramine as a crosslinking agent is made, one of ordinary skill inthe art would appreciate that various other crosslinking agents may alsobe used to crosslink a variety of natural or synthetic polymers to forma pill of the present disclosure.

In a particular embodiment, a natural polymer such as a xanthan gumderivative may be used in combination with a polyetheramine to form thegelatinous structure of the present disclosure. In such an embodiment,the natural polymer may be used in an amount ranging from 2 to 7 llb/bblwhile the polyetheramine is used in amount ranging from about 2 to 15percent by volume.

Wellbore Operations

The pill of the present disclosure may be used in various types ofwellbore operations to isolate two wellbore fluids (or two sections of awellbore fluid) in a wellbore from each other, while simultaneouslycontrollably transmitting hydrostatic pressure therebetween.

In a wellbore having a first wellbore fluid emplaced therein, a pilltreatment comprising a base fluid and polymers may be spotted aparticular region of the wellbore where the gelatinous pill is desired.In a particular embodiment, the base fluid may have a densitysubstantially identical to that of the first wellbore fluid. Uponviscosification of the pill components, the gelatinous structure willisolate an upper region or section of the first fluid from a lowerregion or section of the first wellbore. If desired, a second wellborefluid may be emplaced in the wellbore, and displace the upper section offirst wellbore fluid.

In a particular embodiment, the second wellbore fluid may have a greaterdensity than the first wellbore fluid, thereby allowing displacement ofthe upper section of the first wellbore fluid. By allowing for thecontrollable transmission of hydrostatic pressure across the pill, thebottom hole pressure of the wellbore may be controlled.

The pill of the present disclosure may, for example, be spotted in awellbore during completion operations. Thus, in one embodiment, thewellbore fluid present in the wellbore may be a brine, apotassium/cesium brine in a particular embodiment, having a first givenspecific gravity. A pill comprised of a brine base fluid may be spottedwithin the wellbore, dividing the wellbore into an upper and lowersection. Once the pill is allowed to viscosify or set, the upper sectionof the wellbore fluid may be displaced by a second fluid having aspecific gravity greater than the first fluid. Subsequent completionoperations, including the positioning, repositioning, or removal ofliner(s), logging operations and placement of wireline, and screenplacement may be performed, each involving mechanical interruption ofthe pill, and the spotted pill may remain substantially intact, i.e.,maintain its integrity.

Further, while the above refers to a completion operation, one ofordinary skill in the art would appreciate that the pill of the presentdisclosure may be appropriate in other wellbore operations where a pillthat can isolation and transmit hydrostatic pressure between two fluidsections may be desired. For example, it may be desirable to use a pillof the present disclosure as a lost circulation pill, as a cement plugwhereby the pill may serve as a base on top of which cement may beplaced, or as a kick-off plug for sidetracking.

One of ordinary skill in the art would appreciate that the first andsecond wellbore fluids may be any type of fluid, and that the particulartype may depend on the particular wellbore operation being performed.Thus; in various embodiments, the first and second wellbore fluids mayinclude either an aqueous fluid or an oleaginous fluid, or mixturesthereof, such as those described above.

Additionally, also depending on the particular wellbore operations,additives that may be included in the wellbore fluids disclosed hereininclude, for example, wetting agents, organophilic clays, viscosifiers,fluid loss control agents, surfactants, dispersants, interfacial tensionreducers, pH buffers, mutual solvents, thinners, thinning agents, andcleaning agents. The addition of such agents should be well known to oneof ordinary skill in the art of formulating drilling fluids and muds.

EXAMPLES

The following examples are used to test the effectiveness of the pilldisclosed herein

Example 1 Setting Times

A cesium/potassium formate field mud sample having a mud weight of 2.04sg was used to form various exemplary pills separating a 1.87 sg fluidfrom a 2.08 sg fluid from each other. A saturated potassium formatefluid (1.57 sg) was used to reduce mud weight, and a 2.19 sg cesiumformate fluid was used to increase mud weight. Additionally, a cesiumformate brine was also tested as a base fluid.

Several 1.87 sg pills were tested with various concentrations ofDUO-TEC™ NS, a xanthan gum polymer, and EMI-771, a polyetheramine, bothavailable from M-I LLC (Houston, Tex.), and with various setting times.The base fluid and xanthan polymer were mixed for 5 minutes using aSilverson or Hamilton Beach mixer. The polyetheramine was added and themixture mixed for an addition 2 minutes. To avoid early setting of thepill, the mixture was mixed using a paddle mixer until the pill wasready to be pumped. A small pipe of steel was used to simulate a liner.The results are shown below in Table 1.

TABLE 1 1.87 sg Cs/K mud pill - Setting time at 40° C. 10 kg/m³DUO-TEC ™ NS EMI-771  3% 5% 7% 9% 11% 2 hours No plug. Test No plug.Test Start plugging Soft plug. Test Soft plug. Test stopped stoppedstopped stopped 5 hours — — Soft plug. Test — — stopped 15 kg/m³DUO-TEC ™ NS EMI-771  7% 9% 11%  15%  20% 2 hours Medium plug Mediumplug Medium plug Hard plug Hard plug 5 days — Medium plug Medium plugHard plug Hard plug 17 kg/m³ DUO-TEC ™ NS EMI-771 15% 20%  5 days Veryhard plug Very hard plug 1.87 CsF brine pill 0 Setting time at 40° C. 10kg/m³ DUO-TEC ™ NS 8 kg/m³ DUO-TEC ™ NS EMI-771 10% 8% 10% 8% 1 hourSoft gel Very soft gel Very soft gel Very soft gel 2 hours Medium gelMedium gel Medium gel Medium gel 3 hours Hard gel Hard gel Hard gel Hardgel

When the steel pipe was used to simulate positioning of a liner throughthe pill, a pill comprising 15 kg/m³ DUO-TEC™ NS and 15% EMI-771, whichmay be abbreviated as “the 15/15 concentration,” set up too fast, andthere were difficulties in getting the pipe through the pill. The 12/12concentrations also set too quickly and maintained a semi-hard plug.Thus, it was decided to continue testing with the 10/10 concentration.

Example 2a Separation Ability at 40° C. and at 30 Degrees Inclination

The ability to isolate two fluid sections was investigated by testingthe pill in measuring cylinders. DUOVIS™ Plus NS, a xanthan gumavailable from M-I LLC (Houston, Tex.) was added to the fluids to givena rheology profile closer to the field samples. The specifics of eachtest and results are shown below in Table 2.

TABLE 2 Test Measuring Cylinder Procedure Comments 1.87 sg Cs/K mudpill - Measuring Cylinder - Vertical Test 1 Top: 1.87 sg mud Placed 1.87sg mud in measuring A small interphase on both Mud Pill - 15/15cylinder, sat pill on top of mud with a sides of pill. Difficult toBottom: 1.87 sg mud syringe. Left for 3 hours for pill to set. see thepill due to black Placed 1.87 field mud on top of pill. mud and blackpill. Test 2 Top: 2.08 sg mud Placed 1.87 sg mud in measuring After 2hours set time, the Mud Pill - 15/15 cylinder, sat pill on top of mudwith a more dense mud went Bottom: 1.87 sg mud syringe. Left for 2 hoursfor pill to set. straight to the bottom. Placed 2.08 sg field mud on topof pill. Test 3 Top: 2.08 sg CsF, Placed 1.87 sg CsF in measuring CsFtoo viscous with 10 g/L 10 g/L polymers cylinder, sat pill on top of mudwith a polymers Mud Pill - 15/15 syringe. Left for 2 hours for pill toset. Bottom: 1.87 sg CsF, Placed 2.08 sg CsF on top of pill. 10 g/Lpolymers Test 4 Top: 2.08 sg CsF, Pill placed in 1.87 sg CsF with a CsFtoo viscous with 5 g/L 5 g/L polymers syringe. 2.08 sg CsF placed on topof polymers Mud Pill - 15/15 pill Bottom: 1.87 sg CsF, 5 g/L polymersTest 5 Top: 2.08 sg CsF, Pill placed in 1.87 sg CsF with a OK with 2 g/Lpolymers 2 g/L polymers syringe. Left for 3 hours before Mud Pill -15/15 displacing 2.08 sg CsF on top of pill Bottom: 1.87 sg CsF, 2 g/Lpolymers Test 6 Top: 2.08 sg CsF Let pill set in 1.87 sg CsF. DisplacedIt seemed like the brine Mud Pill - 15/15 2.08 sg pure brine on top.dissolved/diluted the pill. Bottom: 1.87 sg CsF, 2 g/L polymers 1.87 sgCsFormate pill - Measuring Cylinder - 30 degrees Inclination Test 7 Top:2.08 sg CsF, Placed CsF pill in 1.87 sg CsF. Left Interphase on bothsides of 2 g/L polymers for 3 hour to set. Displaced 1.87 sg on pill.Pill too viscous, CsF Pill - 15/15 top with 2.08 sg CsF. problemsgetting “tools” Bottom: 1.87 sg CsF, through. 2 g/L polymers Test 8 Top:2.08 sg CsF, Placed CsF pill in 1.87 sg CsF. Left Interphase on bothsides of 2 g/L polymers for 3 hour to set. Displaced 1.87 sg on pill.Pill too viscous, Mud Pill - 12/12 top with 2.08 sg CsF. problemsgetting “tools” Bottom: 1.87 sg CsF, through. 2 g/L polymers Test 9 Top:2.08 sg CsF, Placed CsF pill in 1.87 sg CsF. Left Looked OK, no problems2 g/L polymers for 3 hour to set. Displaced 1.87 sg on getting “loggingtools” Mud Pill - 10/10 top with 2.08 sg CsF. though. Pill kept the 2.08Bottom: 1.87 sg CsF, CsF on top. 2 g/L polymers

Example 2b Separation Ability at 40° C. and at 30 Degrees Inclination

A 2 meter long pipe having an ID of 5 cm and a Manometer at the bottomwas used to run the same test on a larger scale. The pipe was filledwith a 1.87 sg CsF (added 2 kg/m³ polymers), then a 10/10 pill waspumped and placed in the CsF bring. The pipe was left at a 30 degreeangle at 40° C. overnight. The 1.87 sg brine on top was displaced with a2.08 sg CsF bring (added 2 kg/m³ polymers). After the displacement, thepill was still intact, and there was no channeling of the two fluids.

Example 3 Ability to Transmit Hydrostatic Pressure

A manometer was placed on the bottom of the pipe described in Example 2bto check if the pill would transmit hydrostatic pressure when displacingfrom 1.87 sg CsF to 2.08 sg CsF. As shown below in Table 3, the pilltransmitted the hydrostatic pressure from the upper, more dense fluid tothe bottom of the pipe.

TABLE 3 Measured Pressure Equation 1.87sg CsF + pill + Actual When (ρ +g + h) = pressure Measurement Prior to Displacement 1.87sg CsF + pill +203 mbar (1.87sg CsF × 0.0981 × 0.44) After Displacement 1.87sg CsF +pill + 211 mbar (2.08sg CsF × 0.0981 × 0.44) Measurement Difference 8mbar Control (2.08 − 1.87) × 0.0981 × 0.44 9 mbar

Example 4 Full Scale Test

A test wellbore was displaced to contain a Cs/K Formate fluid having adensity of 1.895 sg at 50° C. The fluid was circulated until an evendensity was measured, and a downole gauge sensor was run on wirelineprior to spotting the pill. A volume of 7.9 m³ at a density of 1.976 sgat 50° C. was prepared using 5.5 m³ CsF brine at 2.127 sg, 0.8 m³freshwater, 0.8 m³ EMI-771, and 75 kg DUOTEC™ NS.

The placement of the pill involved a pump and pull operation, pumping ata rate of 200 Lpm the first third of the volume at 680 meters measureddepth (mMD) before starting to pull while pumping the remaining volumeto end up at 530 mMD as the final volume is pumped. The pipe was rotatedat 30 rpm to ensure even distribution of the pill in the annulus.

A volume of 4 m³ 2.075 sg high viscosity brine was mixed with 10 kg/m³DUOTEC™ NS and also pumping according to the pump and pull operation.The rheology of the fluid was recorded to be 150-120-101-71-30-29 cP (at600-300-200-100-6-3 rpm). The rheology was determined using a Fann 35Viscometer.

The pipe was pulled to 526 m to avoid washing out at the top of theviscosified pill while placing the high viscosity brine. The pipe wasthen pulled to the top of the 2.075 sg brine before displacing theremaining annulus to the same density brine viscosified with 4.5 kg/m3DUOTEC™ NS. Returns of heavy brine were received on surface at expectedpump strokes indicating that the pill successfully isolated the lighterfluid below. The pressure monitored by the gauge on the bottom of thewell was 297.2 bars after the displacement, which corresponded with thewire line logs. The calculated pressure with corrected densities was300.1 bars which indicates that the well was not fully topped up afterpulling out the string.

The following day, a first wire line log was run, followed by a secondlog six days later. The weight of the logging tool was reduced from 170to 110 kg at 30 m RKB. This was probably due to fragments of the pillthat was flushed away as the 2.075 sg fluid was displaced into the hole.A noticeable increased weight on the wireline was experienced at 679 mMDas the tool passed through the pill. The surge and swab effects can beseen on the overview graph shown in FIG. 1. As shown in FIG. 1, thesecond logging run showed identical pressures to the previous loggingrun.

The pill was displaced out of the well three weeks later. The first stepin the pill displacement was running into the hole to a depth of 530 mand rotating at 30 rpm for 5 minutes to break the gels before pumping.The pumps were started slowly to monitor the required pressure to breakthe gels. No pressure increase was observed. The maximum downholepressure recorded while pumping was 310 bar, with an SPP of 37 bar whilepumping 946 Lpm. The maximum pressure while tripping in through thehigh-vis pill was 307 bar at a tripping speed of 130 sec/std. Themaximum pressure increase while tripping in through the pill to 680 mwas 4 bars at the same tripping speed.

The pill was returned across shakers to try to screen out as much crosslinked polymers as possible. The flow rate was increased to 2000 Lpm butreduced to 1000 Lpm to enable screening out as much polymer as possibleon the shakers. There was no visible increase in viscosity as the pillwas returned to surface. The rheology of the fluid was: 55-35-27-19-6-5cP (at 600-300-200-100-6-3 rpm). This indicates that most of the xanthangum polymers were effectively cross linked and screened out rather thancontributing to increased viscosity of the brine. Thus, it was concludedthat the pill could be incorporated into the 1.892 sg mud withoutfurther treatment. Some interference of the interface between the pilland the high viscosity 2.075 sg brine was reported.

A new pill was set from 690 m to 540 m using the same procedure as thefirst pill. However, the second pill was mixed up using a differentprocedure to ensure better mixing of the viscous EMI-771. In the secondpill, 5 kg/m³ DUOTEC™ NS was added before EMI-771 was added, and thefinal 5 kg/m³ DUOTEC™ NS was added after the addition of EMI-771. Theviscosity was lower than the first pill: 127-105-92-71-27-23 (at600-300-200-100-6-3 rpm). The pill was continually circulated to avoidexcessive cross linking.

The 3 m³ high viscosity 2.075 sg mud was displaced at a pump rate of 200Lpm. The high viscosity brine was pumped after pulling up from 530 to452 mMD before commencing to displace in a 2.075 sg fluid at a rate of500 Lpm. After pulling out of the hole, the well was filled up using thekill line.

A “Surge and Swab Tool” available from Seadrill was used to expose thewell to surge pressures as those expected when running a completionscreen hanger assembly through a casing. The tool was run into the holeto 480 m and circulated the 2.075 sg fluid. The SPPs were 4.2 bar at 300Lpm; 8.1 bar at 600 Lpm, and 14 bar at 880 Lpm. The recorded down holepressures varied from 4 to 6 bars. The tool was then run into the holeto 590 m and circulated the 2.075 sg fluid. The SPPs were 5.2 bar at 300Lpm and 6.8 bar at 600 Lpm. The recorded down hole pressures varied from4 to 7 bars. The tool was then run into the hole to 740 m and circulatedthe 1.89 sg fluid. The SPPs were 5.0 bar at 300 Lpm and 5.9 bar at 600Lpm. The recorded down hole pressures varied from 4 to 5 bars. Thepressure increase while running through the pill was 4 to 6 bars. Thecrosslinked pill was displaced out of the hole with a variable pump rateto avoid shaker overflow and as allow as much of the polymers to bescreened out as possible.

Advantageously, embodiments of the present disclosure provide for atleast one of the following. A polymer pill of the present disclosure mayhave sufficient integrity to isolate two fluids in a wellbore from eachother while also balancing the reservoir pressure. A pill havingsufficient integrity may allow for the pill to remain intact duringlogging and completion operations. Further, the pill may allow for theoperator to perform such operations without changing the total fluidvolume, thus reducing logistic challenges and costs. The pill may alsoprovide stability in the hole with no or little tendency of sag over alength of time of at least two weeks. Further, pressure increases due toa heavier fluid may be fully transmitted through the pill to the bottomhole.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1.-10. (canceled)
 11. A method of a wellbore operation, comprising:emplacing a first wellbore fluid in a wellbore; spotting a pill to aregion within the emplaced first wellbore fluid; and allowing thespotted pill to viscosify and separate the first wellbore fluid into anupper section and a lower section, wherein the viscosified pill is agelatinous structure characterized as isolating and controllablytransmitting hydrostatic pressure between the two fluid sections. 12.The method of claim 11, further comprising: emplacing a second wellborefluid.
 13. The method of claim 12, wherein the emplacement of the secondfluid displaces at least a portion of the upper section of the firstwellbore fluid.
 14. The method of claim 11, wherein the second wellborefluid has a greater density than the first wellbore fluid.
 15. Themethod of claim 11, wherein the pill comprises: a base fluid; and atleast two polymers that interact to form the gelatinous structure. 16.(canceled)
 17. A process for completing a well, comprising: emplacing afirst wellbore fluid having a first density in a wellbore; spotting apill to a region within the emplaced first wellbore fluid; allowing thespotted pill to viscosify and separate the first wellbore fluid into anupper section and a lower section, wherein the viscosified pill is agelatinous structure characterized as isolating and controllablytransmitting hydrostatic pressure between two fluid sections; andemplacing a second wellbore fluid having a second density greater thanthe first density in the wellbore, wherein the emplacement of the secondwellbore fluid displaces at least a portion of the upper section offirst wellbore fluid.
 18. The method of claim 17, further comprising:positioning a liner in the wellbore, wherein the viscosified pillremains substantially intact during the positioning.
 19. The method ofclaim 17, further comprising: removing the liner from the wellbore,wherein the viscosified pill remains substantially intact during theremoval. 20.-31. (canceled)